Israelis understood something was up earlier this week when two of the country’s five Iron Dome anti-missile defense systems were moved north to protect Israel’s third largest town, Haifa. The government said the deployment was routine.

This was followed by a flurry of press reports, all quoting anonymous official sources, warning that Israel would not allow Syria and Hezbollah to cross its so-called "red lines."

That meant if Syria attempted to transfer any of its advanced rockets or non-conventional weaponry, such as chemical or biological agents, to Hezbollah, the Shiite militia in southern Lebanon, Israel would halt the move by force.

Ever since the start of the Arab Spring, Israel has had one overriding principle: Stay out. But when that principle came up against its "red lines," the military risk appears to have outweighed the political risk.

Wednesday night a convoy of trucks was attacked by warplanes in Syria, near the border with Lebanon, according to U.S. and regional officials. From Israel – silence. It is believed the convoy was carrying advanced Russian-made SA-17 anti-aircraft missiles, which can hit multiple targets, including fighter jets, helicopters and drones, within 40 miles. They would remove Israel’s critical freedom of flight over Lebanon.

The stakes were raised later by what Syrian state television said was an attack by Israeli warplanes against a military research center northwest of the country's capital, Damascus. There was no confirmation that the target was an advanced weapons collection depot.

From Israel’s point of view, it would be better to stop these weapons from falling into the hands of what it calls terrorists, who could then intimidate all of northern Israel and much of the rest of the country, too, rather than wait for Hezbollah to get them and then have to respond. Prevention rather than reaction.

But the attack implies that Israel feels compelled to join the battle -- not to protect either side in the Syrian conflict but rather to protect its own security. And this move would send a clear message to Israel’s ultimate enemy, the regional power that backs both the Syrian regime and Hezbollah: Iran.

Iran has long threatened to destroy Israel, and Hezbollah is part of its arsenal. Israel choking off the supply of weapons to Hezbollah limits Iran’s future threat against Israel.

Israel never confirms these kinds of attacks. But a comment Tuesday from the head of Israel’s air force didn’t mince words. Major-General Amir Eshel said at a conference that Israel is involved in a “war between wars” and that "this campaign is 24/7, 365 days a year. We are taking action to reduce the immediate threats, to create better conditions in which we will be able to win the wars, when they happen."

Martin Fletcher is the author of "The List", "Breaking News" and "Walking Israel".